The use of MEMS (micro-electro-mechanical systems) sensors is becoming widespread in applications where a small sensor is needed and low cost is important. In applications where the sensor is exposed to harsh environments, such as that in refrigeration and AC systems, a backside entry sensor device is used because the top side of the sensor, which usually contains the piezo-resistive elements and connections to the package, cannot be exposed to the harsh conditions in the environment.
Support structures have a high thermal expansion mismatch between the support material and the MEMS sensor. This mismatch may cause strain, unrelated to pressure, which results in unintended results and errors in the sensor measurements. Accordingly, minimal or stress free installation of the MEMS die is an important aspect of making reliable and better performing pressure sensors.
One method to reduce the strain between the MEMS sensor and the support structure is to use a thermally compliant die attach made of a silicone elastomer. However silicone elastomers may not provide a hermetic seal, thereby allowing gas or liquid to leak into the section of the sensor device having the electronic components therein when high temperatures or pressures are present in the environment surrounding the sensor device. This may cause the sensor device to leak, thereby adversely affecting the sensor readings and yielding inconsistent and inaccurate measurements. In addition, refrigeration systems and sensor systems therein are not allowed any gas or liquid leaks for environmental safety reasons as regulated by the Environmental Protection Agency (EPA).